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June 10, 2009

Mastech Power Supply Forum up and running


Finally we re-installed the forum for Mastech Power Supply again, after we had to shut down last time due to spammers. We apologize for the inconvenience, and hope to use the forum as tool to answer all technical questions. Please visit us at http://mastechpowersupply.com/forum to post any technical questions and get answers from our knowledgeable staff and expert users around the world.

Sean from http://www.mastechpowersupply.com

June 03, 2009

How to Set Current Limit for Mastech CC CV Power Supply?

Setting the current limit for Mastech power supplies is a little bit more complicated compared to setting the voltage limit, especially if you have one of the following situations:

1) your load has internal source of EMF, this includes battery, DC motors, RC cars and trains, any electrochemical systems including plating, etching, and electrolysis, etc.

2) your load might be sensitive or damaged by over voltage, e.g., LED

In the first scenario, you need to make sure to set the voltage to slightly above the maximum EMF from your load, say 0.8V to 1.5V above, and set the current to minimum before connecting the load. Once you connect the load, you can slowly increase the current limit by adjusting the current knob to the desired value. It is highly advised to have a diode put in line with your load (connecting to the positive terminal of the power supply) to prevent the current flowing in the wrong direction and causing damage to the power supply.

In the second scenario, if you can find a simple load like a power resistor or a halogen lamp that can handle the current you want to pass, you can set the current similar to the first scenario (Caution: the power resistor or lamp might be very hot if you are passing large current). Once you are done with setting the current limit, turn the voltage down to minimum, disconnect your load of resistor or lamp, then connect you actual load. you can now slowly increase the voltage while leaving the current setting, just remember to always stop before you raise the voltage too high for your load. If your calculation is correct, then you should be able to stop the voltage knob before actually damaging your load.

If you cannot find a power resistor or lamp, you can still set the current limit you want by following the steps below:

Step 1: before connecting your load, set the voltage limit to safely below what's allowed by your load, and set the current to minimum. The power supply should be in "CV" mode.

Step 2: Connect the load; the Mastech power supply should be in "CC" mode. Slowly increase the current limit, if you are lucky, you can reach the desired current limit before you need to do anything.

Step 3: If you cannot reach the desired current before the power supply switched over from "CC" to "CV", turn the current slightly down so the power supply is switched back to "CC". When in "CC" mode, you can turn the current knob down a little bit more to have a feel about how much turn corresponds to what current change. Using this gut feel, increase the current knob so that it is half way between your desired current level and the maximum you can get without increasing the voltage setting, now the power supply should be in "CV" mode. You can now increase the voltage knob a little, still making sure that it's below what's safely allowed for your load, and stop when the power supply switches from "CV" to "CC". Now you can see what the actual current is. If the current is higher than your desired value, reduce the current setting to your desired value and you are done. If it's lower than what you desire, repeat Step 3 until you get desired current setting.

It sounds complicated, but when you are actually doing it, it only
takes minutes to set it.

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